Over-centre snap acting temperature responsive switch



June 1967 A. J. BENSON 3,327,946

OVER-C ENTRE SNAP ACTING TEMPERATURE RBSFONSIVE SWITCH Filed July 30, 1965 \NVENTOR a lm wg,wb swu'Lm's -AIIQRN Ys United States Patent 3,327,946 OVER-CENTRE SNAP ACTING TEMPERATURE RESPONSIVE SWITCH Anthony John Benson, Maidenhead, England, assignor to Drayton Control Engineering Limited, West Drayton, England, a British company Filed July 30, 1965, Ser. No. 475,995 Claims priority, application Great Britain, July 31, 1964, 30,348/ 64 4 Claims. (Cl. 23648) ABSTRACT OF THE DISCLOSURE An over-centre snap acting switch which is triggered by a thermal expansion probe which is operatively associated with an actuating lever, the switch being provided with an adjustment arrangement for preselection of the temperature at which the switch is activated.

The present invention relates to temperature responsive switching devices of the type in which the device switches from one condition to a second condition in response to a predetermined change in temperature.

Such switching devices are known which include a temperature-responsive probe of the type having an elongated actuating m-ember freely slidably positioned within a tubular housing, the member and the housing respectively being of materials having different coefficients of thermal expansion so that upon change of temperature sensed by the probe there is produced relative longitudinal displacement between the member and the housing. The actuating member acts upon a lever engaging a switching element for causing the element to switch from one position to another upon movement of the lever due to relative displacement of the actuating member and the housing. The described known device has the disadvantage that the actuating member acts directly through the lever to the switching element which thus moves slowly in switching from the one position to the other.

Such slow switching of the element may cause difiiculties in the successful operation of the device because it produces a modulating action and over a fairly wide range of temperature, the switching element is neither in the one position nor the other thereby causing hunting of apparatus the operation of which is controlled by the switching device.

It is an object of the invention therefore to provide a switching device of the type referred to in which the aforementioned difficulty is overcome and according to the invention a temperature responsive switching device comprises a temperature responsive probe operatively associated with an actuating lever which is pivotally secured to a switching element, a spring secured at one end to the switching element and at the other end to an adjustable anchorage, the arrangement being such that in response to a predetermined change in temperature the actuating lever is moved to a position which causes the spring to snap the switching element from a first to a second operating condition.

In a particular form of device embodying the invention the temperature responsive probe operates the ac tuating lever by means of a second lever, one end of which,

engages the actuating lever, the other end being subjected to the action of a compression spring, which applies sufficient loading to the second lever to overcome the force exerted thereon by the first mentioned spring acting through the switching element and the actuating lever, during initial heating or cooling of the probe.

One application of the switching device of the present invention is in the control of the operation of the by-pass 3,327,946 Patented June 27, 1967 valve of a catalytic silencer associated with the control of air pollution by automobile exhaust systems.

In the use of such a catalytic silencer, it is usual to provide a by-pass valve for diverting the exhaust gases from the catalytic silencer to a conventional silencer when the temperature of the catalyst rises to a predetermined temperature for example 700 C. The bypass valve is operated by reduced pressure from the engine intake manifold to hold the valve open to the catalytic silencer under normal running conditions, the connection from the intake manifold to the valve including a temperature responsive switching device in which the switching element is adapted to close a port to atmosphere when in its normal position and to open the port to atmosphere when in its other position. The temperature sensing probe of the device extends to the catalyst bed of the silencer and when the temperature of the bed exceeds the predetermined temperature, the switching element switch-es to its other position thereby breaking the vacuum connection to the by-pass valve which then releases to divert the exhaust gases from the catalytic silencer to the conventional silencer.

Alternative constructions of switching device according to the invention for use in a catalytic exhaust system will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a sectional elevation of one construction of the device; and

FIGURE 2 is a similar view of a modified form of operating mechanism for the device.

As shown in FIGURE 1 the device comprises a housing 1 defining a chamber 2 having an inlet port 3 adapted to be connected to the intake manifold of the engine, an outlet port 4 adapted to be connected to the by-pass valve of the catalytic exhaust system, and a port 5 leading to atmosphere. A temperature sensing probe indicated generally at 6 depends from the housing 1 and is adapted to be positioned in, or closely adjacent, the catalyst bed of the silencer. The probe 6 comprises a metal tube 7 within which there is freely positioned an actuator member 8 formed of a material, for example a ceramic, having a coefficient of thermal expansion appreciably different from that of the tube 7.

An actuating lever 9 is fulcrummed at one end on 21 depending lip ll) of the housing 1 and is engaged by the upper end of the actuator member 8 at a short distance from the lip 10 so that relative displacement of the actuator member 8 and the tube '7 due to change of temperature will cause the lever 9 to swing about its fulcrum. The other end of the lever is upwardly turned as at 11 and pivotally supports one end of a switching element 12, the other end of which mounts a closure member 13 adapted to engage and to close the port 3 or the port 5 depending upon the position of the element 12 as hereinafter described.

Both the actuating lever 9 and the switching element 12 are lengthwise slotted to accommodate a tension spring 14 secured at one end to the switching element 12 and at its other end to the lower end of a screw threaded post 15 extending downwardly into the chamber 2. The relative disposition of the lip It), the lever 9, the switching element 12, and the post 15 is made such that upon the temperature sensed by the probe 6 rising to a predetermined value, the switching element 12 is caused to snap from the position shown in FIGURE 1 in which port 5 is closed and the port 3 is open, to its other position in which the port 5 is open and the port 3 closed. In this other position of the switching element therefore, the connection to the engine intake manifold is closed and the connection to the by-pass valve is vented to atmosphere through the port 5 and the by-pass valve releases to divert the exhaust gases from the catalytic silencer to the conventional silencer.

The temperature at which the snap action of the switching element occurs can be varied by lengthwise adjustment of the screw threaded post 15 in the housing 1.

To avoid wide angular movement of the snap-action lever on pre-travel while the probe is warming up to the predetermined operating temperature, it may be desirable to arrange that the lever has a slow rate of movement with respect to temperature change during pre-travel and a rapid movement immediately prior to and including the operating temperature.

One such arrangement is shown in FIGURE 2 in which the actuator member 8a acts on the actuating lever 9a through a further lever 16. The actuating lever 9a is pivoted on a stud 17 and the further lever 16 is fulcrummed on the actuator member 8a, one end of the lever 16 engaging the actuating lever 9a adjacent the stud 17 while the other end of the lever 16 is formed in a U shape and is acted upon by a compression spring 18 surrounding the post 150. The said other end of the lever 16 is apertured as at 19 so as freely to accommodate a reduced portion 20 of the post 15a, the said reduced portion terminating at its lower end in a shoulder 21 against which, as will hereinafter be described, the apertured end of the lever 16 abuts during operation of the mechanism.

The spring 18 applies suficient loading to the lever 16 to overcome the force exerted thereon by the spring 14a acting through the switching element 12a and actuating lever 9a, so that during initial heating of the probe and as the actuator member 8a is displaced downwardly relative to the housing 1a, the lever 16 is pivoted in an anticlockwise direction about its point of engagement with the lever 9a until its apertured end abuts the shoulder 21 of the post 15a. Upon continued downward relative displacement of the member 8a, the lever 16 then pivots in a clockwise direction about its point of engagement with the shoulder 21, thereby releasing the pressure exerted on the actuating lever 9a by the said one end of the lever 16 to permit the actuating lever 91; to pivot about the pin 17 until the switching element snaps to its other position.

Because of the change in the lever ratio when the pivotal movement of the lever 16 changes from anti-clockwise to clockwise, the latter movement with respect to dis placement of the member 8a is more rapid than the former so that the snap action of the switching element is effected at a more precisely determinable temperature sensed by the probe.

It will be noted that the diflerence between the temperature at which the changeover of direction of movement of the lever 16 occurs and the temperature at which snap action of the switching element 12a is efiected, is determined by the relative positioning of the shoulder 21 and the point of anchorage of the spring 14a on the post 15a, and is substantially independent of the longitudinal adjustment of the post 15:: relative to the housing 1a.

The device described may also include an electrical switch (not shown) operable conjointly with the switching element and connected in the circuit of an electric lamp mounted for example on the dashboard of the vehicle for indicating to the driver of the vehicle when the catalytic silencer is being by-passed.

The port conveniently will be connected to a source of dry atmosphere within the body of the vehicle thereby to prevent the ingress of dirt and water into the cham her 2.

It will be understood that the invention is not limited to the specific construction described nor in its application to catalytic exhaust systems. For example the switching element may be adapted to effect switching between two electrical contacts for controlling the operation of an 4 electrical circuit. Again, although in the specific example described the spring 14 in FIGURE 1 and 14a in FIG- URE 2 is a tension spring, the desired snap action may be obtained by using a compression or trident type of spring.

I claim:

1. An improved temperature responsive switching device including a housing, a thermal expansion temperature probe mounted on said housing, an actuating lever operating associated with said probe, a switching element pivotally retained on said actuating lever, a stationary anchorage mounted in said housing and a spring secured at one end to said switching element and at the other end to said stationary anchorage, in which the improvement consists of the feature that said stationary anchorage is adjustably mounted within said housing thereby to vary the temperature at which said probe moves said actuating lever to a position in which said spring causes over-centre snapping motion of said switching element from a first to a second operating condition.

2. A temperature responsive switching device as claimed in claim 1 in which said probe operates said actuating lever by means of a second lever, one end of which engages said actuating lever, the other end being subjected to the action of a compression spring which applies sufiicient loading to said second lever to overcome the force exerted thereon by said first mentioned spring acting through said switching element and said actuating lever, during a predetermined range of heating or cooling of said probe.

3. A temperature responsive switching device as claimed in claim 1 in which said housing of said device is provided with an inlet port, an outlet port, and a venting port, said switching element being adapted to close said venting port in one position and to close said inlet port in its other position.

4. A temperature responsive switching device including a housing, a thermal expansion temperature probe mounted on said housing, an actuating lever operatively associated with said probe, a switching element pivotally retained on said actuating lever, a stationary anchorage mounted in said housing, a spring secured at one end to said switching element and at the other end to said stationary anchorage and a second lever, one end of which engages said actuating lever, the other end being subjected to the action of a compression spring which applies sufficient loading to said second lever to overcome the force exerted thereon by said first mentioned spring acting through said switching element and said actuating lever, in which said housing is provided with an inlet port, an outlet port and a venting port, and in which said stationary anchorage is adjustably mounted within said housing thereby to vary the temperature at which said probe moves said actuating lever, by means of said second lever, to a position in which said first spring causes over-centre snapping motion of said switching element from the position in which said venting port is closed to the position in which said inlet port is closed.

References Cited UNITED STATES PATENTS 1,898,419 2/1933 Birtch 200-137 2,303,029 11/ 1942 Dillman 74-110 2,469,757 5/1949 Watson 251-75 X 3,166,247 1/1965 Malone et al 23648 3,233,057 2/1966 Aschwanden 200-67 WILLIAM J. WYE, Primary Examiner.

ALDEN D. STEWART, Examiner. 

1. AN IMPROVED TEMPERATURE RESPONSIVE SWITCHING DEVICE INCLUDING A HOUSING, A THERMAL EXPANSION TEMPERATURE PROBE MOUNTED ON SAID HOUSING, AN ACTUATING LEVER OPERATING ASSOCIATED WITH SAID PROBE, A SWITCHING ELEMENT PIVOTALLY RETAINED ON SAID ACTUATING LEVER, A STATIONARY ANCHORAGE MOUNTED IN SAID HOUSING AND A SPRING SECURED AT ONE END TO SAID SWITCHING ELEMENT AND AT THE OTHER END TO SAID STATIONARY ANCHORAGE, IN WHICH THE IMPROVEMENT CONSISTS OF THE FEATURE THAT SAID STATIONARY ANCHORAGE IS ADJUSTABLY MOUNTED WITHIN SAID HOUSING THEREBY TO VARY THE TEMPERATURE AT WHICH SAID PROBE MOVES SAID ACTUATING LEVER TO A POSITION IN WHICH SAID SPRING CAUSES OVER-CENTRE SNAPPING MOTION OF SAID SWITCHING ELEMENT FROM A FIRST TO A SECOND OPERATING CONDITION. 